快速测定啤酒中异戊醇含量

采用气相色谱-质谱联用法,配合溶剂延迟并选择适当的质谱扫描范围以及Postrun迅速升温、迅速加大载气流量,以直接进样的方法快速测定了啤酒中异戊醇的含量。通过比较内标法和外标法对定量准确性和速度的影响,找到一种简单快速的对啤酒中异戊醇定量的方法(用内标法每个样品只用4min),并且测定了市售17种啤酒中异戊醇的含量。     

适配体传感法快速测定啤酒中赭曲霉毒素A

应用自组装方式,构建了金纳米粒子/核酸适体/氨基碳量子点荧光传感赭曲霉毒素A高灵敏检测方法。在pH 3.0酒石酸-HCl缓冲溶液中,巯基修饰的赭曲霉毒素A核酸适体在金纳米粒子表面自组装,形成金纳米粒子/核酸适体复合物,再在pH 7.0的磷酸盐缓冲溶液中,氨基碳量子点在金纳米粒子/核酸适体复合物上自组装,形成金纳米粒子/核酸适体/氨基碳量子点复合物荧光传感检测体系。金纳米粒子的摩尔吸光系数大、能带宽使其具有强烈的荧光猝灭功能,氨基碳量子点形成金纳米粒子/核酸适体/氨基碳量子点后发生荧光猝灭, 此时体系的荧光为背景荧光,其强度记为F₀;由于金纳米粒子/核酸适体/氨基碳量子点复合物荧光传感检测体系中核酸适体对赭曲霉毒素A具有特异性识别与结合功能,向金纳米粒子/核酸适体/氨基碳量子点复合物荧光传感检测体系溶液中加入赭曲霉毒素A后,赭曲霉毒素A则与复合物中核酸适体立即发生特异性结合并释放出氨基碳量子点,体系荧光恢复,其荧光强度记为F。依据体系荧光强度的变化(F-F₀)与赭曲霉毒素A浓度之间的关系,建立赭曲霉毒素A核酸适体荧光传感检测方法。研究了金纳米粒子和核酸适体摩尔比、孵化时间、pH等因素对传感器性能的影响,确定了最优条件为金纳米粒子∶核酸适体t为1∶190、孵化时间为6 min、pH 7.0时;在最优条件下,赭曲霉毒素A浓度在0.005～1.00 ng·mL-1范围与体系荧光强度变化呈良好线性关系,线性回归方程为：F-F₀=6.499+211.6c(c为赭曲霉毒素A的浓度,单位：ng·mL-1),相关系数r为0.995 5,按3倍标准差与工作曲线的斜率的比值(3σ/k)计算,得检测限为3 pg·mL-1。在实际样品中的回收率在93.3%～108.9%,相对标准偏差小于5%,能满足啤酒样品中赭曲霉毒素A快速检测要求。对13个市售啤酒样品进行检测,其中6个样品检出赭曲霉毒素A,污染率为46.15%。受污染样品的赭曲霉毒素A含量在0.008～0.63 ng·mL-1范围。该荧光传感法检测赭曲霉毒素A具有灵敏性好、特异性高、常见真菌毒素无干扰、方法简单、快速,便于大众化推广应用的优点。     

A sensitive method for the determination of nitroamines in alcoholic beverages

Summary Nitrosamines in alcoholic beverages and malted barley were analysed by adsorption from the gas phase onto a porous polymer trap of Chromosorb 104 and subsequent desorption of the trapped compounds directly to a gas chromatograph fitted with glass capillary column and alkali-FID. The detection limit for NDMA was 0.05 g/l in beer samples and 0.3 g/kg in malted barley.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Tracing the origin of beer samples by NMR and chemometrics: Trappist beers as a case study

An NMR and chemometric analytical approach to classify beers according to their brand identity was developed within the European TRACE project (FP6‐2003‐FOOD‐2‐A, contract number: 0060942). Rochefort 8 Trappist beers (47 samples), other Trappist beers (76 samples) and non‐Trappist beers (110 samples) were analyzed by ¹H NMR spectroscopy. Selected NMR signals were measured and used to build classification models. Three different classification problems were identified, namely Trappist versus non‐Trappist, Rochefort versus Non‐Rochefort, and Rochefort 8 versus non‐Rochefort 8. In all the three cases, both a discriminant and a modeling approaches were followed, using partial least squares discriminant analysis (PLS‐DA) and soft independent modeling of class analogies (SIMCA), respectively, leading to very high classification accuracy as evaluated by external validation. Information regarding chemical composition was also obtained: Trappist beers contain a higher amount of formic and pyruvic acids and a lower amount of acetic acid and alanine with respect to non‐Trappist ones. Rochefort beers turned out to have also a higher content of propanol and isopentanol with respect to non‐Rochefort samples. Finally, Rochefort 8, shows the highest content of pyruvic acid and the lowest content of gallic, fumaric, acetic acids, adenosine, uridine, 2‐phenylethanol, GABA, and alanine.     

啤酒中N-亚硝胺的SPME-GC-MS分析

研究了固相微萃取-气相色谱-质谱(SPME—GC—MS)联用方法检测啤酒中的N-亚硝基二乙胺(NDEA)、N-亚硝基吡咯烷(NPYR)、N-亚硝基二丁胺(NDBA)，采用聚二甲基硅氧烷／二乙烯苯(PDMS／DVB)萃取头，对影响固相微萃取效率的萃取时间、搅拌速度以及萃取方式等进行了优化，在优化实验条件下，方法的线性范围在12．5～250μg／L之间，相关系数r为0．9971～0．9995，检出限分别为NDEA4．50μg／L，NPYR8．99μg／L，NDBA2．27μg／L，NDBA回收率为86％～96％，相对标准偏差6．296～8．996，该法简化了前处理步骤，快速、方便．结果满意。     

Solid phase extraction of amines

The objective of this paper is to provide information about solid phase extraction (SPE) as an alternative to liquid-liquid extraction of amines from several matrices. Different sorbents ranging from non-polar phases, such as C₁₈ silica to more polar such as cyanopropylsilica (CN) have been tested for analysis of aliphatic amines as monoamines, diamines and polyamines. Phenylalkylamines such as amphetamine or methamphetamine and heterocyclic amines such as histamine or cephalosporins (which also contain a carboxylic group), have also been studied. The different steps involved in the extraction procedure have been tested (conditioning, retention, pre-concentration, washing and elution) in order to obtain extracts free of interferences and enough sensitivity. C₁₈ silica (100 mg) was selected as optimal phase with recoveries nearly of 100%. The elution of more polar amines was performed in acidic conditions while less polar amines required organic solvents. Cephalosporin retention was performed in acid condition by using disk cartridges EM C_18, which gave better selectivity. The optimised clean-up procedures have been discussed to the quantification of the corresponding amines in real samples (urine, water and beer). The accuracy and precision were outlined.     

Sample stacking effects and large injection volumes in micellar electrokinetic chromatography of ionic compounds: Direct determination of iso-α-acids in beer

Summary The possibility of using large injection volumes in micellar electrokinetic chromatography (MEKC) has been evaluated. With charged compounds effective focusing is observed. For a given liquid sample, the ratio of sample-to-buffer conductivity is decisive in obtaining this effect. The direct analysis of iso--acids in beer, thus omitting prior extraction, is demonstrated. Data on quantitative analysis are presented.     

Analysis of methylglyoxal in water and biological matrices by capillary zone electrophoresis with diode array detection

We describe a new method for the determination of methylglyoxal in water and biological matrices, using o-phenylenediamine as derivatizing agent and solid-phase extraction followed by capillary zone electrophoresis with diode array detection. 25 mM sodium phosphate running buffers at pH 2.2, 30 kV, and 25 degrees C allowed the best instrumental conditions for the optimum separation of methylglyoxal in a suitable analytical time (< 10 min), using an uncoated fused-silica capillary of 75 microm inner diameter and an effective length of 45.1 cm with an extended light path and the wavelength set to 200 nm. Under optimized instrumental conditions, good reproducibility of the migration time (< 1.1%), precision (< 5%), an excellent linear dynamic range from 0.1 to 3.6 mg/L (r(2) = 0.9997), and low limits of detection (7.2 microg/L) were obtained for methylglyoxal measurements, using the internal standard methodology. Assays on laboratory-spiked tap and ground water samples allowed a remarkable accuracy, presenting yields of 95.0 +/- 4.3 and 94.0 +/- 1.1%, respectively, and good performance to determine methylglyoxal in beer and yeast cells suspensions matrices was also obtained at trace level. The present methodology is a cost-effective alternative for routine quality control analysis, showing to be reliable, sensitive, and with a low sample volume requirement to monitor methylglyoxal in water and biological matrices.     

Preparation of novel solid-phase microextraction fibers by sol-gel technology for headspace solid-phase microextraction-gas chromatographic analysis of aroma compounds in beer

3-(Trimethoxysilyl)propyl methacrylate (TMSPMA) was first used as precursor as well as selective stationary phase to prepare the sol-gel-derived TMSPMA-hydroxyl-terminated silicone oil (TMSPMA-OH-TSO) solid-phase mircroextraction (SPME) fibers for the analysis of aroma compounds in beer. TMSPMA-OH-TSO was a medium polarity coating, and was found to be very effective in carrying out simultaneous extraction of both polar alcohols and fatty acids and nonpolar esters in beer. The extraction temperature, extraction time, and ionic strength of the sample matrix were modified to allow for maximium sorption of the analytes onto the fiber. Desorption temperature and time were optimized to avoid the carryover effects. To check the matrix effects, several different matrices, including distilled water, 4% ethanol/water (v/v) solution, a concentrated synthetic beer, a "volatile-free" beer and a real beer were investigated. Matrix effects were compensated for by using 4-methyl-2-pentanol as internal standard and selecting the "volatile-free" beer as working standard. The method proposed in this study showed satisfactory linearity, precision and detection limits and accuracy. The established headspace SPME-gas chromatography (GC) method was then used for determination of volatile compounds in four beer varieties. The recoveries obtained ranged from 92.8 to 105.8%. The relative standard deviations (RSD, n = 5) for all analytes were below 10%. The major aroma contributing substances of each variety were identified via aroma indexes.     

Approach for non-destructive pigment analysis in model liquids and carrots by means of time-of-flight and multi-wavelength remittance readings

Non-destructive spectroscopy in the visible and near infrared wavelength range has been introduced for analyzing absorbing compounds in fruit and vegetables. A drawback of the method appears due to the measuring principle, where photons detected in the diffusive tissue are influenced by the sample absorption but also scattering properties leading to variation in the photon pathlength. In the present work, distribution of time-of-flight reading was used to calculate the effective pathlength between source and detector. Using this information in addition to the spectral intensities obtained with common continuous wave spectroscopy, Lambert–Beer law was applied for analyzing absolute pigment contents.The method was tested for liquid phantoms mimicking the optical properties of fresh fruit and vegetables. Lambert–Beer law using a constant pathlength as well as combined application of the intensity at a specific wavelength and the effective pathlength resulted in low calibration errors with r² > 0.98. Applying the two calibrations on phantoms mimicking changes in the scattering properties resulted in validation results of r² = 0.47 and 0.64, respectively.Improved results by using the effective pathlength were confirmed on real-world samples. The carrot carotenoids analysis resulted in validation results of r² = 0.66 and 0.74, respectively, while the measuring uncertainty was reduced from 18.10 to 9.62%.Multivariate calibrations using the entire carrot spectra and data pre-processing aiming the reduction of scattering effects resulted in slightly lower measuring uncertainty by comparison. In the sensor fusion approach proposed, however, no expensive spectrophotometer is required and the phenomenon of varying optical properties of the sample is characterized.